[time-nuts] Re: HP Z3801A project update

[ed breya]

I found a spare Oncore VP GPS RX unit in the parts department last week, 
and tried it out in the Z3801A. It would not track, even after quite 
some time in use. The original would pop right up almost immediately, 
after warm up.This one had some slight differences from the original, 
around the antenna connector area. It was originally rigged up with the 
rechargeable Li cell option - I remember removing it years ago. I added 
a jumper to carry the external battery supply line in, to make it the 
same as the other. After several swap-outs with the good one, with no 
improvement, I did a direct comparison, and deleted a couple of parts 
from the bad one, making it look "exactly" like the good one. I 
suspected the problem was in the memory chip enable/reset circuit, or 
the left over Li cell charging part.

On this last round of checking, it acted just like before, no good. It 
seemed to operate, and all parts showed OK in SatStat, but it just would 
not track any satellites, even though it seemed to recognize and list 
them. I checked the antenna power and such, and all looked OK.

I was even planning to send a message about this to the group, asking 
for ideas, but finally, after quite some time (maybe an hour), it seemed 
to miraculously come alive, and showed satellite tracking. My theory is 
that either the power up reset wasn't working, or the memory was so 
corrupted (yet remembered enough) from all the different trials and part 
changes, that it just took a while to gradually clear enough of it to 
work. During earlier testing, I found responses to queries like 
"invalid/data corrupted," to paraphrase.

So anyway, it seems to be working right now. I'll have to put through 
some power up and down tests and such, to make sure it really is good to 
go. It's comforting to have a spare of this part, since it appears 
replacements are getting hard to find.

Ed